Carb/exhausht question

[jaimes-duran]

Hi everyone. I'm sure there' more than one simple answer to this question. So I'll start by telling you the problem. I noticed my pipes were blue and took them off for a cleaning. Then I looked into the exhaust holes to see how they looked. 3 of the cylinders were black and 1 was white and coroded looking. So I start the bike and fire is shooting out of both of the outside exhuast holes. Obviously this is what is causing the blue pipes. My question is what is causing the fire? And how do I fix it. The bike runs fine by the way ans is a 79 xs1100 special. Thanks

[BigDick]

Just guessing here. . . I'd say your exhaust valve is either not sealing, allowing the combustion to blow by, or your valve timing is off. Maybe it slipped a tooth letting it open just a bit too soon. Some more knowledgable person whill chime in soon.

[DiverRay]

What grade of gas are you using? If the bike is stock, then REGULAR is all you should need. If you have been using high octane for a while, you probably have a LOT of carbon built up in the combustion chamber. With the bottom of the air box removed, spray seafoam into all four carbs, and then spray a LOT into all four until it dies. Do this with a warm engine, and let it set for about 20 minutes. start it again, (this may take a few tries) and run it till warm again. Rev it up to about 4K while warming up (not steady, just bring it up and let it drop back to idle).
This should remove any carbon, and help a bit with the running. I would also check your valve clearance, as you may have one or two exhaust valves too tight.

[jaimes-duran]

I'm just using regular fuel. Is this a MAJOR problem or common? Will my engine eventually blow or die? I will definitely try the seafoam? I don't know much about the valve timing etc. I am definitely not a mechanic. Thank you guys a lot for the info I appreciate it. Any other imput?

[DGXSER]

Definitely check the valve clearances. Typically, if the cam chain skips a tooth that would cause a valve to be open like that it would also bend the valves, which would happen on ALL four cylinders.

However, I have seen where only one valve could be bent, but not the others.

[tarzan]

You didn't mention any backfiring going on, so I doubt you have a bent valve.
With no headers it will run lean and spit fire.
Running lean with exhaust installed, which was where this started, could be a vacuum leak.I.E.- leaking carb holder(boot) or vacuum cap or shaft seals.
It could just need an air mixture adjustment.
I think more investigation is in order.After all, you said it runs fine right?
Check the plugs to see how they are burning.That should be a good indication how it is really running.
BTW, do you have stock exhaust or aftermarket?Most aftermarket exhaust are single walled pipe and will blue.
Rick

[Larrym]

Pyrotechnics: Gene Simmons???

It's been a long time since I had the courage to start/run a motor with no exhaust connected to the head. Must have been a real exciting event: noise and the fire shooting out.

First, the one cylinder which looked "white and coroded looking" would indicate to me that the cylinder was running too lean. Too lean can cause a number of serious problems with the piston and the valves. As this is the only cylinder with this condition/symptom then I'd investigate that carb for something wonky.

The other cylinders looking "black" would indicate an overly rich fuel/air mixture. Different problems would happen with the piston/valves but IMHO not as serious as the overly lean condition presented before. Again I'd have the carbs investigated/adjusted as a first step.

The exhaust ports should mirror what one would see on the spark plugs. Tan or light brown is a healthy indication. If in fact the fuel/air mixture is overly rich (as in the three black ones...) it's likely that the fuel didn't get enough air to burn completely. Then when the exhaust valve opens this partially burnt but still burning mixture would be exposed/ejected to the fresh oxygen in the outside air: Flamethrower Style.

Time to either read the tech tips for cleaning/adjusting your carbs and do it yourself or locate another member who has time and a warm garage.

[Ivan]

Fire coming out an exhaust port on an engine with no exhaust is normal. Ever watch rail dragsters? Those things spit fire out four to six feet high. The reason is that the optimal power output is not at a point where all fuel burns in the combustion chamber, and the burning completes in the exhaust.

This is what a catalytic converter takes care of in modern vehicles. The converter stores heat and at a critical temperature the rare earth metals create a catalytic reaction much like a flameless lighter.

I would be more concerned about the two that didn't shoot fire out, they are probably running lean.

The cylinder that has white corrosion in it, are you sure it isn't ash? Lots of times a small oil leak into the combustion chamber (valve seals or the rings starting to go) will make a whiteish gray ash build up. Look at your spark plug on that cylinder and see if the plug looks like that as well.

This is a plug with oil deposits on it:



Taken from here.

[XJOK2PLAY]

I agree w/ Larry & Ivan.

Sounds like some carb adjustments/ synching may be in order... and don't be concerned about seeing fire when the header pipes are removed. Totally normal.

Blue pipes... could also depend on type of exhaust pipes your using. Stockers were double walled, and helped prevent the blueing. Some aftermarkets are only single walled, and blue no matter what you do, or how well tuned your engine is.

I just wouldn't recommend running that engine too long w/o the pipes in place... you're changing the amount of air in the mixture... hence the fire... right at the valves when overlap occurs... and you can burn the edges of the valves from the XSive heat if you run it too long. A little shouldn't be a problem... running it down the road under load w/ no pipes... a different story!

(Not to mention how deaf you'll be, and how angry the neighbors will get! LOL)